The way that I understand the a99 limiter is that when a range is set it will basically ignore the objects that are out of that range and not even attempt to focus on them. If it truly works as described it may well be much more useful than any lens limiters that I have used as they may attempt to focus on something that you may not want and will just stop sooner because of your setting and return quicker rather then having to run through the entire focusing range.